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RESEARCH PRODUCT

Analysing the origins of the strong variability of impact by Tischeria ekebladella, a common mining moth on oak leaves.

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Tischeria ekebladella (Lepidoptera : Gracillariidae) is a common moth with its caterpillar often mining oak leaves, morerarely chestnut leaves. As a rule, the mining impact of the species exhibits strong variations according to locations,inviting to investigate quantitatively the respective contributions of the three main factors that regulate the level of minesdensity within host. As the direct monitoring in the fi eld of these governing factors is very diffi cult (when not virtuallyimpossible), we use a newly designed procedure (“MELBA”) which allows tracing back to these factors indirectly, on thebasis of posterior, easily recorded data (in terms of the histogram of the distribution of the numbers of mines per hostleaf).The respective contributions to the mine impact variability of Tischeria ekebladella, according to locations, wereestimated by this procedure as: (i) 49% due to variations of host-leaf quality ‘α’, (ii) 45% due to variations of mothers’local density (density of mothers’ visits to host-leaves ‘μ’) and (iii) a small contribution only (6%) due to variation ofclutch-size ‘nc’. The estimated degree of mothers’ selectivity among host-leaves prior to egg-laying is rather strong(proportion of rejected host-leaves from 50% up to more than 80%). Yet, the host-leaf quality proves having no signifi cantinfl uence upon the clutch-size in this species. Also, the average quality of leaves within a given oak tree seems to haveno appeal on females and thus, no signifi cant infl uence on the local density of Tischeria mothers.